In general, though, I like to keep my mechs up front, except SOME artillery mechs that should be placed so they can range left/right or forward/back the most, to be able to target the most tiles.

I like to give vek my mechs to target, so they won't target buildings and I can - if necessary - ignore them to deal with greater threats. i also like to if possible put my mechs on empty lines so if they do move, the vek is shooting at nothing, and not a building.

There are many other things, like baiting blobbers and spiders with mechs that shoot something back while firing (like the flame artillery), but they are too numerous to really go into in detail, and I'll forget a lot of them.

Your mechs should be the targets, not the buildings. Your mechs can and will move, your buildings can not. All HP a mech has is expandable, except the last. As a rule of thumb, burn through HP if it provides you any advantage.